1. Field of the Invention
The present invention relates to an engine starting device including a mechanism for shortening, when a restart request for an engine is issued while the engine is still rotating by inertia immediately after idle stop, a restart time by bringing a pinion gear into meshing engagement with a ring gear of the engine without rotating a starter motor for the pinion gear during rotation of the ring gear even in the case where the rotation of the ring gear is in a reverse direction.
2. Description of the Related Art
In a conventional engine starting device (hereinafter referred to as starter), a start operation is carried out while an engine is stopped. Thus, a pinion gear meshes with a ring gear while the ring gear is not rotating. However, in a system for carrying out idle stop for reducing fuel consumption, a restarting property is secured by meshing the pinion gear with the ring gear even when the ring gear is rotating.
For example, at the moment when the idle stop is just started and the engine is not stopped yet, if a restart is requested, or if it is necessary to reduce a period for a restart from a stop state, while the ring gear is rotating, the ring gear is meshed in advance with the pinion gear.
As described above, as a method of meshing the pinion gear with the ring gear while the ring gear is rotating, there is known a method of meshing the pinion gear by supplying an electric power to thereby adjust the speed of the starter motor of the pinion gear so that the pinion gear is synchronized with the RPM of the ring gear (for example, refer to Japanese Patent Application Laid-open No. 2002-70699). Moreover, there is known a method of carrying out, by providing a mechanism for synchronization in advance, synchronization up to a predetermined difference in RPM by friction of a portion of the mechanism, and then meshing gears with each other (for example, refer to Japanese Patent Application Laid-open No. 2006-132343). Further, there is known a method of facilitating the meshing by devising the pinion shape (for example, refer to Japanese Patent Application Laid-open No. 2009-168230).
However, the conventional technologies have the following problems.
The ring gear decelerates while rotating by inertia after the engine stops, and in this case, the RPM becomes zero while pulsating due to a fluctuation in torque caused by compression and expansion by pistons. Thus, for example, as described in Japanese Patent Application Laid-open No. 2002-70699, for synchronizing the RPMs of the ring gear and the pinion gear with each other by the engine starting device (starter), thereby meshing those gears with each other, a complex configuration is necessary. Specifically, there is a need for a complex configuration for acquiring or predicting the RPMs of the ring gear and the pinion gear, and, based thereon, for controlling the starter to mesh the ring gear and the pinion gear with each other.
In the complex configuration, the timing to push the pinion gear and the timing to start rotating the pinion gear are important. Even after the rotation of the pinion gear is started, however, it takes a long period of time for an RPM of the pinion gear to increase up to a predetermined RPM. Further, it also takes a predetermined period of time to bring the pinion gear into meshing engagement with the ring gear by pushing the pinion gear. Further, the predetermined period of time is varied. Therefore, the meshing engagement between the pinion gear and the ring gear by rotating the pinion gear in synchronization with an engine RPM is practically difficult to achieve with a simple system.
Moreover, when a speed of decelerated rotation of the engine is high, the increase in RPM of the pinion gear cannot follow the speed of rotation of the engine. Thus, at the time when the pinion gear is pushed to come into contact with the ring gear, there arises a phenomenon in which the ring gear rotates in a reverse direction. In the case where the reverse-rotation phenomenon occurs, a direction of the rotation of the motor is required to be reversed. Therefore, a motor system and control for the motor rotation become complicated, and therefore are difficult to realize.
Further, during a period in which the engine is decelerating while rotating by inertia with pulsations, the engine starts rotating in the reverse direction depending on a piston position immediately before the engine is stopped. In order to cause the pinion gear to follow the reverse rotation, the motor is required to be rotated in the reverse direction. Even in this case, performance and control of the motor itself become complicated, and therefore are difficult to realize with a simple system.
In view of the variation which actually occurs as described above, the RPMs for meshing engagement can be brought into synchronization to achieve the meshing engagement only under certain limited conditions.
On the other hand, for example, as described in Japanese Patent Application Laid-open No. 2006-132343, by providing a configuration in which the pinion gear and the ring gear are synchronized in RPM by a synchronization mechanism in advance to be then brought into contact with each other, the ring gear and the pinion gear can be synchronized with each other in RPM by a simpler configuration. However, a gear ratio of the pinion gear to the ring gear is generally present at a level of ten times for reducing the size of the motor, and the pinion gear and the ring gear are not arranged coaxially due to a restriction in terms of a dimensional configuration.
Thus, the synchronization is carried out while a friction surface of the synchronization mechanism for bringing the pinion gear into contact with the ring gear is always slipping, and it is difficult to realize a complete synchronization in which the phases are matched as well. Therefore, the meshing engagement is difficult in the reverse direction, and hence there is a need to take appropriate measures, such as prohibition through control.
Moreover, in the synchronization mechanism, when the ring gear and the pinion gear are in contact with each other after the synchronization, except for a case where the phases are matched with each other by chance, a slip is generated between the ring gear and the pinion gear, and the ring gear and the pinion gear mesh with each other when the phases thereof are matched. In this way, in the configuration employing the synchronization mechanism, after the synchronization is realized by the slip, the pinion gear and the ring gear are brought into contact with each other.
As a result, there are a problem of noises and wear upon the contact and a problem in that a friction surface is additionally necessary for the synchronization, resulting in requirement of an additional space. Also in view of the configuration, the space becomes larger than that for the conventional pinion gear and ring gear, and therefore it is difficult to realize the simple meshing engagement.
Therefore, as a method of simply meshing the pinion gear and the ring gear with each other, for example, in a case where the synchronization mechanism is used, as described in Japanese Patent Application Laid-open No. 2009-168230, in order to facilitate the meshing between the pinion gear and the ring gear, it is conceivable to devise a shape of ends of the pinion gear, thereby providing a chamfer or the like on the tooth end. As a result, according to Japanese Patent Application Laid-open No. 2009-168230, a space portion realized by the chamfering can be inserted, and a guiding effect by the surface contact is realized.
On this occasion, according to Japanese Patent Application Laid-open No. 2009-168230, for the meshing in a state in which the ring gear is stopped, the guiding effect by the chamfering is provided. However, in a case where a relative RPM of the pinion gear is different while the ring gear is rotating, a collision of both the gears as a result of the contact of the chamfered portions generates a force component of pushing back the pinion gear in the axial direction. Therefore, the chamfer is disadvantageous in the case where the ring gear is rotating.
In this way, when the pinion gear is meshed while the ring gear is rotating, the noises, a decrease in service life due to wear, and the delay in starting which is caused by a loss in the meshing time occur unless more secure synchronization and phase matching are carried out at the moment of the contact.
Particularly, in a case where the RPM difference is large when the pinion gear and the ring gear mesh with each other, when the teeth are rubbed against each other for a long period of time without synchronization, the noise level becomes higher.